Concrete Slab

1) The 5cm slab may be handy to provide level support for the polystyrene sheets. If insulation is foamed in place, there does not seem to be any need for the slab...certainly no structural need.

2) Whether or not the insulation is adequate depends on the temperature inside the storage units and the ambient temperature on site. There is not enough information to respond to this.

3) The average load on the upper slab is very low, but I would be inclined to use a minimum of 15cm slab to allow for possible concentrations of load from the jacking equipment. Control joints should be placed at about 6m centres to control cracking. Alternatively, you could use more reinforcement and omit the joints.

It is a little late for me Gary, but I will reply in the AM.

TMF

Dear Sir

i am not a civil engineer; however from my long experience working in the field of hotel maintenance i can advise regarding the finishing oh these cold rooms which should be in ceramic tiles thickness +10mm; and preferred dimensions 15cmx15cm.

dont not apply epoxy as a finishing surface it will not last the 10 years.

Mohamed Esmat

Hi Gary,

I won't comment on the civil specs part of the concrete floor, however we provide tailored network temperature monitoring for cool store (chiller/freezer) applications. We use a Scada application, primarily for monitoring/logging for food storage quality compliance and with alarming function for equipment problem/failure warning. We have noted that in freezer applications, heating elements are installed within the upper concrete floor to prevent the sub-foundation freezing and the ground raising, thereby uplifting and destroying the concrete floor. We sometimes incorporate a temperature sensor and alarm for the concrete floor heating. The freezer temperature is usually around -20C and the concrete is usually kept to around +1C. If yours are only chillers (-3 to +5C) it is probably not a concern but if for a freezer it is worth considering bfeore you pour the concrete. The floors for the freezers are usually 100mm concrete+50-75mm polystyrene+150mm concrete and these floors take fork/turret trucks.

For what it is worth.

AussieBob,

I agree that insulation and underslab heating are important considerations, particularly in cold climates with frost susceptible soils below the slab. This project is to be built on desert sand which suggests (a) it is warm and (b) the soil is not susceptible to frost heaving. It would seem to me that more information is required to determine the insulation and/or heating requirements.

Hello

This has to be designed as slab on grade, you cant have that 55m in one span. I recommend to have smaller pieces of slabs same 4x4 or 5x5m slabs with expansion / construction joints between the slabs. If you go for any longer / bigger pieces you cant do with 12m thickness and moreover you will start getting cracks; also you may need Comp & Tension steel too in case you exceed 4 to 5m spans.

Please consider 15cm thickness with mesh 12dia both ways 170mm C/C top only with clear cover not less than 60mm, slab size 4x4m. OPC is recommended normally, in case you suspect suphate attacks as is normal in Saudi Arabia desert sands, you may use SRC Type-V, 460 kg/Cu.m.

Good morning Gary,

I think that beginning this explanation from the top surface down will make the matter clearer, by the time we get to the lowest area of compaction.

The top layer of concrete is floating on foam. Foam has no structural integrity and is there only for it's insulating purposes. So the top layer of concrete must be strong enough to carry the loads that you will place on it. Realize that this entire loaded weight will be carried on several square inches of area of the pallet wheels until you set the load down. Therefore the top slab must be strong enough to carry said load as if it were going to remain on this small area indefinitely, if not you will experience the problem of having the palled wheels punch holes in the upper surface. You will also experience the issue if expansion and contraction. This is best dealt with through the addition of "temperature bars placed about 1 1/2" below the surface. These bars are typically 3/8" thick. Other structural reinforcing pars, usually about 5/8" thick are generally laid out in a grid pattern designed by the structural engineer. However as you may be trying to eliminate that expense and have your local contractor do the entire job, I suggest that this grid for the thicker re-bars be laid out on a crossing pattern about 1" each way, and remember that it to must be surrounded on all sides by at least 1 1/2" of concrete. This area of the work must be designed so that the areas that would represent each compartment for storage is constructed as if it were isolated, and have the area around all sides thickened as if it were a typical house slab on grade construction. The expansion and contracting of concrete causes it to crack, so the idea is to make it crack where said cracks can be controlled. This is best accomplished by pouring these sections separately, in an every other pattern. Do not pour the newer concrete directly against the previous pour. Place 1/2" foam sheets between the new and previous pour. This will permit the separate slabs to move with out walking, by compressing the foam. The walking action occurs when the concrete expands and pushed against the outside slabs and then when contraction occurs a crack opens that gradually fills with material solids that do not compress and the next expansion pushes the out ward slabs a little more. This is a continuing process and the most movable areas of concrete will gradually separate to expose larger gaps between these individual areas. It is just what happens with all concrete. Sooner or later.

Next will be the issue of having the foam attempt to float to the top of the upper layer of concrete when it is placed. The foam must be anchored, glued or otherwise secured down so that it cannot float, if not, it absolutely will under any circumstances.

Said foam is to be placed on the lower layer of concrete. It must be thick enough to remain strong enough so that it will not disintegrate through natural cracking. This area must have a perimeter footing. reinforced with 5/8th in re-bar, likely two will be enough for this purpose. Where ever you will be supporting the walls of your cool above, you should provide an interior footing, often referred to as a thickened slab, only in these areas, and these thickened areas should also be reinforced with re-bar. Constructing the floor in this manner makes the foundation fully bearing on the compacted fill, helping it to carry the loads over a much wider area. It is more commonly called a grid foundation.

This manner of construction will cause the two different concrete surfaces, the upper and lower to have what we in the business call a cold joint meaning the upper and lower areas could move or not move independently of each other. For your needs this is good.

As for the compaction issue, you referred to "Construction in the Desert." This could mean that you are building on a dry lake bed, a sand pile or large sandy area, or maybe a mixture of rocks and sand. In all cases using a blended material of some soil cement and the available screened local materials will help you to reach the proposed compaction results with much less effort.. Frankly, you can pound on dry desert sand until the steers grow old enough to butcher and never obtain the desired compaction called for in the plans. The addition of thousands of gallons of water will sometimes work but in the desert, I don't see that much water available for compaction purposes.

Remember that you are first constructing a foundation that is for all intended purposes supporting the loads above with out being actually attached to the floating upper flooring.

As for the sealing of the upper surface, grinding the surface smooth so that the rocks show through and then sealing the surface with an epoxy material designed for long lifespan under your intended conditions will usually work best and help preserve sanitation requirements.

TooMuchFun

First of all

You need to know what kind of soil under the building/structure.

second , you need to have continuous slab under those partitions.

also where is this structure?

Alot depends on the climate.

I am a structural engineer, in US

I might help,

Pls give more specific info.

Good luck.

Take a look at post no. 7 guest,

I think I covered most any issue that the thread poster may encounter given the info provided. You are quite correct to challenge the condition regarding the soil. I have constructed buildings in almost any general type of soil classification, tho the names differ with locations the consistencies for the various grades of courses and fines and the ability to be compacted are "generally" predictable. Having encountered a great number of differing soil conditions and uses for foundations and slabs , including the one intended here, I believe that the inclusion of multiple floating slabs, separated with the foam expansion material will best serve the ultimate owner.

Any time that I have constructed acres of concrete, poured on grade I have always recommended that these slabs be cushioned around all sides to prevent the slabs from walking. In fact I have been retained as a professional witness at a number of hearings where issues regarding the Contractors responsibility vs the Engineers responsibility seem to be in conflict.

TooMuchFun

TooMuchFun -

Brilliant descriptive write up - I do it your way and just can CONFIRM that this way works - BUT - as an engineer you MUST have an inspection when the steel is set, first pour is done, on site quick slump check, float check at correct time and on second inspection that the "foam" is fixed with steel nails and the rest as above - contractors take chances. The Joints / Cuts needs to be sealed by an Industrial sealer that expands/contracts to the conditions stipulated by an application

Just a quickie - rule of thumb - block by block method or if a strip pour is done then the joint cuts / blocks = 30 x slab thickness = 150 mm floor; 30 x 150 = 4,500 x 4500 mm blocks / strip joint cuts within 36 hrs maximum.

AussieBob -

I enjoyed you contribition, very well explained. I sincerely hope others in the field will take notice of your valuable contribution.

Thank you, both of you guys.

Gentlemen,

I want to thank each and every one of you for your comments and advice. I do apologize for not getting back to you with the information you require, but being out here in Southern Darfur, communication is somewhat erratic, and at the best of times, we are only able to log on for about 10 minutes, before the signal is interupted in one way or another.

Back to the question at hand, the whole reason for this conctrete slab is to support a freezer/chiller room that will have it's own insulated floor. This entire unit will only be resting on the slab. The temperature of the unit will in no way affect the slab, as the slab will not be exposed to the various temperatures inside the unit. (well it will to some extent, but I don't think this will adversly affect the supporting slab.)

All I really want to know is.......will it be necessary to start with a 5cm slab, followed by the polyurathane insulation, and then the 10cm slab re-enforced with rebar? We are trying to save costs (obviously) and don't want to use the first slab if it is not absolutely necessary.

Once again, your comments will be greatly appreciated.

Best regards,

Gary Cameron.

Hello Gary,

If you are going to do this on the cheap, and durability is not an issue, I suggest that you drop the individual units into a recessed concrete foundation that includes 4" of poured in place concrete as a monolithic placement. Drop your completed storage units in the recess and add enough concrete, about 3 more inches to bring the level of the floor in each cooler up to just a little more than the surrounding concrete level and slope it downward at the entrances to accommodate flushing when cleaning is needed.

What you really need to do is spend a little money hireing an engineer to save you lots of head aches and future costs in maintainence and repairs.

TMF

10 cm is NOT enough - 150 mm at 30Mpa - with Ref 245 min RF - I am from Africa, I know the condition - +43°c to -3.0°C in 24hrs - nope keep it as you implies with the good advice of the TooMuchFun as a VERY serious consideration. Also AussieBOB - you CANNOT imagine the Refrigeration Effect Loss through the floor, in the end you will sit with too little refrigeration input too because of heat losses.

And in AFRICA you uses 150 mm panels, forget 75 and 100 mm. Electricity is scarce and expensive in Africa and will become more scarce.

Even RSA's electricity network under the current regime is falling into shatters after a Rolls Royce was handed to them, unfortunately all other service too - REMEMBER - THIS IS AFRICA - a TOTAL different world - you must expect the worst at all times in all circumstances.

Here is two sayings- ADAPT or DIE, & You can take them out of the bush, but you cannot take the bush outa them. Harsh words, but unfortunately true.